With continuous scaling down of semiconductor devices, the conventional SiO2/poly silicon gate configuration is gradually being replaced with the high-K gate dielectric/metal gate configuration. Accordingly, the gate first process is gradually being replaced with the gate-last process.
In the gate last process, a sacrificial gate stack is used for device manufacture. Then, the sacrificial gate is removed and replaced with a real gate stack. However, a space left after removing the sacrificial gate stack is becoming smaller and smaller, so it becomes more and more difficult to fill the real gate stack into the space.